The present invention relates to a printed circuit board drilling machine, and more particularly to a pressure foot for a printed circuit board drilling machine using a drill bit.
Japanese Utility Model Unexamined Publication No. 61-124313 shows a pressure foot for a printed circuit board drilling machine for effecting a drilling for a printed circuit board.
FIG. 9 in the present application shows an example of a printed circuit board drilling machine which comprises a bed 1 and a table 2 slidably supported on the bed 1 and driven by a drive apparatus (not shown). Drills 3 are prepared in holders fixed to the table 2. A column 5 is provided on the bed 1 so as to straddle the table 2. A spindle carriage 6 is slidably supported on the column 5 and is driven by an action of a Y-axis drive motor 7. A spindle saddle 8 is slidably supported on the spindle carriage 6 and is driven by an action of a Z-axis drive motor 9. Each rotor shaft 10 is supported on the spindle saddle 8 and is drivingly rotated by an action of a motor 11. A pressure foot 12 is mounted on a cylinder block 13. Reference character W designates a printed circuit board (hereinafter simply referred to as a board). The board W is fixed on the table 2 by standard pins P.
In such an arrangement, the table 2 and the spindle carriage 6 are moved relative to each other in X-Y directions to thereby locate the boards W and the rotor shafts 10. Thereafter, the spindles are moved in the Z-direction and the drilling is effected by the drills held at the associated rotor shafts 10.
FIG. 10 shows a structure of the spindle portion of the printed board drilling machine in which the cylinder block 13 is fixed on the spindle saddle 8. A large diameter hole 14 and a flange 15 radially inwardly projecting from one end of the hole 14 are formed on the cylinder 13. The hole 14 is in fluid communication with a pressurized air source through a pipe 16.
A spindle 17 is fitted in the cylinder block 13 and is adapted to rotatably support the rotor shafts 10. The motor 11 is supported at one end of the spindle 17 and is coupled with the rotor shaft 10. A chuck 18 is fixed to a lower end of the rotor shafts 10 and in turn holds the drill 3. A piston or ram 19 has a flange 21 for slidable moveable in a space defined by the hole 14 of the cylinder block 13 and the spindle 17.
The pressure foot 12 is fixed to one end of the piston 19. Formed on a side wall of the pressure foot 12 is a suction port 22 connected to a vacuum suction source (not shown). In a bottom wall of the pressure foot 12, there are formed grooves 23 for sucking air during the drilling.
With such a structure, the compressed air held at a predetermined pressure is supplied from the pipe 16 to thereby move the piston 19 toward the lower end of the cylinder block 13. The discharge of the air from the pressure foot 12 is effected through the suction port 22. At this time, the air is sucked from an opening portion formed at the lower end of the pressure foot 12 and is discharged through the suction port 22 as shown in FIG. 11.
Under this condition, when the spindle saddle 8 shown in FIG. 9 is lowered, the pressure foot 12 once holds the board W as shown in FIG. 12. Thereafter, the drill 3 is depressed into the board W to thereby perform the drilling operation.
In this case, the air is sucked into the pressure foot 12 through the grooves 23 and thereafter is discharged through the suction port 22. The flow of air sucked through the opening portion and the grooves 23 of the pressure foot 12 makes it possible to discharge cut chips and to cool the drill 3.
In general, a dust collector is used for collecting cut chips as the vacuum suction source, and a pressure within the pressure foot 12 during the drilling is about 200 mmHg.
In a conventional machine, the drilling is effected while the printed circuit boards W are held by the pressure foot 12, whereby it is possible to prevent the vibration and lift of the printed circuit boards W during the drilling to thereby perform a high quality drilling and at the same time to prevent damage to the drill 3.
On the other hand, the cut chips or powders generated during the drilling are to be collected in the dust collecting device.
However, since the grooves 23 of the pressure foot 12 are small in size, it would be impossible to insure a sufficient amount of air flow during the drilling and also impossible to sufficiently cool the drill 3 and to remove the cut chips or powders.
In particular, in the case of the drill having a small diameter of 1 mm or less, it is likely that the cut chips clog the grooves of the drill and the discharge of the cut chips will be insufficient. For this reason, in the case where a deep-drilling with a larger ratio of the bore diameter to the depth thereof is desired, a thrust load and a radial load imposed on the drill 3 during the drilling are increased, so that breakage by bending or torsion is likely to occur.
In addition, if the grooves for the drill 3 are clogged by the cut chips, not only the cooling effect of the drill 3 will be worse but also the heat amount generated by the friction between the chips and the inner wall of the bore will be increased, so that the temperature of the drill 3 would be considerably elevated. Furthermore, since air kept at room temperature is simply blown to the drill 3, the temperature of the drill 3 would be not sufficiently reduced. Thus not only the wear of the drill 3 is markedly increased but also various problems such as an increase of the surface roughness of the inner wall of the hole drilled, a generation of burr at the inlet/outlet of the hole and an increased amount of smear.
Furthermore, a part of the cut chips generated during the drilling is left at a circumferential edge portion of the hole as a burr, or otherwise is adhered once to the inner wall of the pressure foot and the drill, and thereafter can fall on the printed circuit board.
If, under the condition that the chips left on the printed circuit board enters into a space between the pressure foot and the circuit board, the drilling is adversely effected with the printed circuit board being held. Hence the quality of the inner wall of the hole drilled is degraded due to the lift or vibration of the board, and at the same time, it is likely that the drill will be damaged.
Accordingly, in order to overcome these defects inherent in the conventional machine, an object of the invention is to provide a pressure foot for a printed circuit board drilling machine in which a drilling stroke is reduced to thereby reduce a drilling time, the drill is sufficiently cooled and the removal of the chips may be effected without fail.